Fusion fixing apparatus employing heat and pressure

Abstract

An apparatus for fusion fixing thermoplastic toner images on an image carrier by use of heat and pressure, comprising a heatable fixing roller comprising a first extension tube, a first cylindrical cover surrounding the first extension tube and being comprised of an elastic, heat- and permanent deformation-resistant material, and a first tubular sleeve pulled over the first cylindrical cover, with the first tubular sleeve having a polytetrafluoroethylene surface; a pressure roller mounted adjacent to the fixing roller, the pressure roller comprising a second extension tube, a second cylindrical cover surrounding the second extension tube and being comprised of an elastic, heat- and permanent deformation-resistant material, and a second tubular sleeve pulled over the second cylindrical cover; an apparatus for selectively engaging and disengaging the pressure roller against the fixing roller; and an arrangement for driving the pressure roller and the fixing roller at the same speed when the rollers are engaged, whereby the image carrier material is transported between the rollers without blurring the images thereon.

What is claimed is: 
     
       1. An apparatus for fusion fixing thermoplastic toner images on an image carrier by means of heat and pressure, comprising: a heatable fixing roller comprising a first extension tube, a first cylindrical cover surrounding said first extension tube and being comprised of an elastic, heat- and permanent deformation-resistant material, and a first tubular sleeve pulled over said first cylindrical cover, said first tubular sleeve having a polytetrafluoroethylene surface;   a pressure roller mounted adjacent to said fixing roller, said pressure roller comprising a second extension tube, a second cylindrical cover surrounding said second extension tube and being comprised of an elastic, heat- and permanent deformation-resistant material, and a second tubular sleeve pulled over said second cylindrical cover;   means for selectively engaging and disengaging said pressure roller against said fixing roller; and   means for driving said pressure roller and said fixing roller at the same speed when said rollers are engaged, whereby the image carrier material is transported between said rollers without blurring the images thereon.   
     
     
       2. An apparatus according to claim 1, further comprising means for applying an anti-adherence medium to said fixing roller. 
     
     
       3. An apparatus according to claim 1, wherein the material comprising said first and second cylindrical covers has a density of 0.24-0.30 g/cm 3 , a breaking strength of 260 kilo-Pascal at 200° C. and of 350 kilo-Pascal at 175° C., and a breaking tension of 60 percent at 200° C. and of 75 percent at 175° C., so that it is sufficiently elastic that the contact surface between said fixing roller and said pressure roller in the engaged position is substantially planar during passage of the image carrier material between said rollers. 
     
     
       4. An apparatus according to claim 1, wherein said driving means includes a drive shaft on which said first extension tube of said fixing roller is mounted, first friction wheels arranged near the front of the driving shaft, a shaft on which said pressure roller is mounted, corresponding second friction wheels mounted near the front surfaces of said pressure roller shaft and engaging said first friction wheels when the pressure roller is in the engaged position, whereby the pressure roller is carried along at the speed of the fixing roller. 
     
     
       5. An apparatus according to claim 4, wherein the first friction wheels of the driving shaft and the second friction wheels of the pressure roller shaft include overriding clutches which are mounted on the driving shaft and on the pressure roller shaft. 
     
     
       6. An apparatus according to claim 1, wherein said first sleeve comprises a thin-walled, flexible polytetrafluoroethylene tube. 
     
     
       7. An apparatus according to claim 6, further comprising glass fibers incorporated into said tube in order to increase its mechanical strength. 
     
     
       8. An apparatus according to claim 6, further comprising corrosion-resistant, helical steel strips incorporated into said tube. 
     
     
       9. An apparatus according to claim 6, wherein said first sleeve comprises an extruded polytetrafluoroethylene tube. 
     
     
       10. An apparatus according to claim 1, wherein said first cylindrical cover comprises an open-cell foamed silicon material. 
     
     
       11. An apparatus according to claim 1, wherein said first cylindrical cover comprises an expanded rubber with a density between about 0.2 and 1.0 g/cm 3 . 
     
     
       12. An apparatus according to claim 2, further comprising a heating chamber surrounding a portion of the circumference of said first tubular sleeve and two radiators in the interior of said heating chamber arranged near the points where said fixing roller enters and leaves said heating chamber. 
     
     
       13. An apparatus according to claim 2, further comprising a heating chamber surrounding a portion of the circumference of said first tubular sleeve, wherein said applying means is arranged opposite to the heating chamber and comprises a container for the antiadherence medium, and a wetting wick which issues from said container and rests against part of the circumference of said first tubular sleeve. 
     
     
       14. An apparatus according to claim 13, wherein the wetting wick is loosely inserted into the interior of the container and the end of the wick which is outside of the container rests against a wick carrier and is tensioned by a tension spring. 
     
     
       15. An apparatus according claim 1, wherein said means for selectively engaging includes means for providing a relatively planar contact area therebetween.